Bridge resistor construction



Aug- 10, 1954 R. D. RICHARDSON 2,686,245

BRIDGE RESISTOR CONSTRUCTION Original Filed May 24, 1945 4f N EEE IN VEN TOR. P05597 0. /c//A/msa BMU y Wma@ Patented Aug. 10,4 1954 BRIDGE RESISTOR CONSTRUCTION Robert D. Richardson,

signor to The Hays Cor Ind., a corporation of I Original application 1 Claim. l

This invention relates to a gas measuring device. More particularly it relates to a device for measuring the oxygen content of a gas.

This application is a division of my co-pending application, Serial No. 595,569, filed May 24, 1945, now Patent No. 2,568,384, Nov. 10, 1953.

The primary object of this invention is to provide a simple, accurate, sturdy and durable device for measuring oxygen.

A further object is to provide a practical device for determining the oxygen content of a gas by measuring the cooling effect of a movement of gas upon a heated wire positioned in a heterogeneous magnetic field.

A further object is to provide a device of this character which may be operated from either a direct current or a low frequency alternating current power supply.

A further object is to provide a device of this character having means for controlling the ow of gas in a predetermined pattern therein for measurement purposes.

A further object is to provide a device of this character having a novel thermal element of rugged construction.

A further object is to provide a device of this character having a novel, sturdy and thermally stable test cell.

A further object is to provide a device of this character having novel and simple means for effecting zero adjustment.

Other objects will be apparent from the description, drawings and appended claim.

In the drawings:

Fig. 1 is a vertical sectional view of the device, with parts illustrated diagrammatically.

Fig. 2 is a transverse horizontal sectional view taken on line 2 2 of Fig. 1.

Fig. 3 is an enlarged side view of the heating element of the device.

Fig. 4. is a still further enlarged transverse sectional view taken on line 4 4 of Fig. 3.

It is known that molecular oxygen possesses paramagnetic properties of a higher order than all other gases excepting NO. Likewise it is known that the heat conductivity of a paramagnetic gas is reduced in a homogeneous magnetic iield. The latter condition limits to only about 1% the total effect or change in thermal conductivity for the full range of oxygen to be measured, that is, the range from to 100% oxygen `concentration in the gas sample. This eiiect is too small to be used as an accurate indication of the oxygen content of a gas in a practical gas measuring device of reasonable cost and with acceptable precision and sensitivity.

La Porte County, Ind., as-

poration, Michigan City, ndiana May 24, 1945, Serial No.

Divided and t 10, 1952, Serial No. 265,

his application January 846 (Cl. 21H- 63) However, if a heated Wire is positioned in a heterogeneous magnetic eld, it is cooled when surrounded by a paramagnetic gas. The cooling action results from the flow of gas past the heating element. The paramagnetic gas adjacent to the heating element and heated thereby has a lesser magnetic susceptibility than its surroundings and consequently it tends to flow to an area of lesser iiux density and is displaced in the magnetic iield by cooler gas of greater magnetic susceptibility. This results in the flow of gas which has a cooling effect upon the heating element. The cooling effect due to the movement of the gas is opposite to the effect due to the thermal conductivity of the gas, but is much greater and therefore can be measured with greater accuracy by apparatus of lower cost than required for measuring thermal conductivity as mentioned above. The present invention utilizes this principle and reaction for the measurement of the oxygen content of a gas.

Referring to Figs. 1 to 4, the numeral I0 designates a test cell which preferably constitutes a block of brass or other non-ferrous material. The material of which cell I0 is constructed is preferably selected for its thermal stability and general ruggedness. The cell has a plurality of spaced parallel vertical passages therein, preferably arranged in line as shown in Fig. 2. Passages II and I2 are interconnected at their upper ends by a longitudinal passage I3, and passages I4 and I 5 are interconnected at their upper ends by a longitudinal passage I6. The lower end of each of the vertical passages II, I2, I4 and I5 communicates with a horizontal gas now passage I'I. A pair of aligned and opposed inwardly tapering horizontal bores I8 are formed in cell I0 and communicate with passage II intermediate the height thereof. A pair of tapered iron pieces I9 iit within the bores I8 with their tips substantially flush with said passage. A C- shaped magnet 20 is adapted to embrace the cell I0 with its opposite pole portions so positioned adjacent to or in engagement with the pieces I9 as to magnetize them. The magnet 2U may be pivotally mounted upon any suitable support (not shown) by means of pivot studs 2I.

Two heating elements 22 are provided in the device. Element 23 constitutes a measuring element and is positioned in passage Ii. Element 26 constitutes a comparison element and is positioned in the passage I5, aithough it can be positioned in passage it ii desired. IThe construction of the two heating elements is the same and they have the same heating properties. The construction is best illustrated in Figs. 3 and 4.

A support 25 is formed of electrical insulating material such as glass, and may be of cup shape as shown. Support 25 is mounted in a suitable opening in the block i in communication with the desired passage of the group of passages li-i6. A wire stem V26 extends longitudinally through the support 25 in which 'it is iixedly se cured. The upper portion of stem 26 projects from the support to provide a terminal 21. The lower portion 28 of the stem 26 projects below the support 25 and supports a glass tube or sheath 29 which is melted in place therearound. A coil of wire 33 is wound around the 'tube 29. The entire unit is then glazed with the same type o1 glass used for tube 29 to provide an outer coat or sheath 3i. A second wire stem 32 extends longitudinally through and is secured to support 25 in spaced relation to stem 28. The upper end of stem 32 projects above the support 25 to provide a terminal 33 and the lower end portion 34 of the stem is Ysecured to the glazed coat 3l to cooperate with stem 26 to support the depending heater unit. The coil Sti is connected at its upper end to stern 32 and at its lower end to stem ,portion 28.. The length of the depending heater portion of each element is preferably such that its lower end or tip is positioned at the level of the pole tips i9 of the magnet 2U, the tip of element 23 terminating between magnet tips i8 in passage H as shown.

The terminals 2 and 33 of the two heater ele ments are connected in separate legs 35 and 35' of a Wheatstone bridge circuit Whose remaininglegs Sii and 3l have impedances or resistances 38 therein. The bridge circuit is connected to any desired source of power 39, which may be either direct current or alternating current, by leads 4t which are connected at points 4l and 42 between branches 3E and 35 and between branches 35 and 3'?, respectively. A lead 43 is connected to the bridge circuit between branches 35 and 35 and a lead et is connected to the bridge circuit between branches 36 and 3l. A recorder 45, provided with an amplifier, or an indicator, is connected to the bridge circuit by leads 43 and lili.

In the operation of the device, passage il is connected by any suitable means (not shown) with the source of gas whose voxygen content is to be measured so that a continuous flow of sample gas is supplied to the device. The gas sample passes into the passage i l, and the oxygen content is attracted into the heterogeneous' magnetic eld in the space between the pole pieces i9 of magnet 2e by reason of its paramagnetic properties. At that point the gas is heated by the heating element 23, and the heated oxygen loses its attraction to the magnetic field. Cerise quently, the comparatively cold oxygen from passage il continually pushes the heated oxygen upwardiy through the passage l i and a net iiow of gas is maintained. A free and unrestricted path for this flow oi gas .is provided by the passages i2 and it, for return of the gas sample to passage il. The comparison heating element 2t is positioned identically with relation to the gas sample in a branch flow lpath provided by pasi sages ill, i and it.

By virtue of the properties of oxygen in a magnetic field, i. e., the attraction of cold oxygen to a magnet and the loss of such attraction upon heating thereof, the rate of iiow of gas in passage i i and along the heating element 23 is greater than in the passage containing the comparison heating element 24. The increased gas ow serves to cool the heating element 23 somewhat. 'I'his changes the electrical value of the heating element 23 and unbalances the normally balanced bridge circuit to permit operation of the recorder 45 in direct proportion to the percentage of oxygen present in the gas sample. If there is no oxygen present inthe system, there is still a ilow oi gas due to the thermal effect of the heating elements 23 and 24 thereon. However, this effect is balanced at the two elements 23 and 24. This general flow or" gas reduces the time lag that would be necessary for direct diffusion.

The pivot mounting of the magnet so that it can be swung away from the members I9 accommodates quick and simple zero adjustment of the device.. In other words, by swinging the magnet the members E9 are demagnetized, and the Wheatstone bridge and the recorder can be checked for bridge balance and zero setting by energizing the device, because the conditions at the measuring element 23 and at the comparison element i4 are then the same. The adjustments so made are not altered by the subsequent return of the magnet to `position to rei-.magnetize members i9.

The use of a body iii 'formed or" brass or other thermally stable non-ferrous material, and the provision therein of the iron members i9 above described, are important features of the invention. rilhermal stability and inherent ruggedness of strength result from the use of the brass block. Hence the device, and especially the test block, does not have to be handled under laboratory conditions, but can be used in a boiler room or at any location convenient to the apparatus to which the gas under test is 'derived Danger of breakage is minimized, as are thermal fluctuations which would adversely aiect reading. The passages in the block provide for a control of the pattern of gas now for maximum eiliciency and sensitivity and for avoidance of errors in the results recorded or indicated. Thus, the control of the gas flow pattern facilitates accurate calibration of the instrument.

The construction oi the heating elements is of critical importance because it permits operation of the device by direct current or by low frequency alternating current, for example, 60 cycle current- In either instance, the effect of the current in the magnetic field is neutral because the current passes through the coil 3d in one direction relative to the magnetic neld and through the stem or wire 2S in the opposite direction relative to the held. The use of heating elements of the type common in thermal conductivity units could not be resorted to in a device requiring a magnetic field for its operation because of the eiect of the field on the current unless a Very high frequency of alternating current is used. The latter expedient would overcome this effect of the magnetic field but would have an inherent tendency to introduce vibration, particularly at a recorder or indicator which includes amplifying means, so that the accurate reading or operation of the recordel or indicator would be impossible. Like-'- wise, use of a nigh frequency would require shielding, whereas ordinary cond-uit wiring can be used with this device. Other advantages of the heata ing element construction are that the elements are thermally stable because the thermal con'- ductance common in single lead encased elements is materially reduced; that collection of moisture is less troublesome with this construction than with prior types of heating elements in thermal conductivity devices; that a glass can be selected Whose thermal expansion exactly matches that of platinum er" which the heating wires are formed; the heating element is strong and rugged. The construction of this heating element may be utilized for other types of thermal. Conductivity devices than that here illustrated and described.

While the preferred embodiment or" the invention has been illustrated and described herein, it will be understood that changes in the construction may be made Within the scope of the ap.- pended claim Without departing from the spirit of the invention.

I claim:

A heating element for use in a gas measuring device, comprising a support formed o insulation material, a pair of spa-eed conductors extending through and projecting from said support, a rigid elongated insulation member supported by said conductors, and a pair of spaced heating wires imbedded in and electrically separated for their major extent said member, each of said Wires being eleetrieally connected to one of said conductors at one end, said Wires being connected to each other at their opposite end said s pport being cup-shaped and being adapted te nt in and form a closure for a passante, said conductors e-X- tending through said support and simstantaily parallel to the axis thereof.

References Cited in the file of this patent UNITED STATES PATENTS Nnniher Name Date 845,413 Haagh Feb. 25, l 1,860,541 iebler May 31, 193 2,216,375 Minter @et l, 1940 FOREIGN PATENTS Naineer Ceuntry Date 537,155 Great Britain June ll, 1941 

